1. Field of the Invention
The present invention relates to a memory device which holds data temporarily and can be used as a data processing device, and a driving method thereof.
2. Description of the Related Art
As for data processing devices such as micro processing units (MPUs), improvement of operation frequency and miniaturization of elements have been researched and developed in order to improve performance and reduce power consumption. On the other hand, power consumption of data processing devices due to leakage power caused by miniaturization of elements is increased.
Such a problem of increase in power consumption is tried to be solved by a technique for reducing power consumption such as a power gating technique in which power supply is stopped in a short period during which power supply is not needed. Further, in recent years, a technique, which is called normally off computing, in which even in a circuit which always needs power supply, needed data is saved in a nonvolatile memory device and power is supplied only when necessary has attracted attention.
Patent Document 1 discloses a structure in which a magnetoresistive random access memory (MRAM) is used as a nonvolatile memory device, data of a microprocessor is saved in the MRAM when power supply is stopped, and the data of the microprocessor is restored when the power supply is restarted.